Production of isoolefins



Dec; 1966 H. E. VON ROSENBERG 3,290,405

PRODUCTION OF ISOOLEFINS Filed NOV. 7, 1962 2 Sheets-Sheet 1 lSO-OLEFINS 5 L N S A l Q M F 6 A R E 2 R W 0 L 2 f F m N 0 3 k A L 4 u 3 8 0g TFLIIZ Li 3 l l L 4 R 2 l I A s\ ll 9 fll U 5 W I\L\\ R E o v L T 8 C M m M: w M m D l .l E E R G E w R S 0 RE T F m v V E 2 O 8 R w w 2 6 I 0 l v 4 m REGENERATOR CATALYST FIG.

ATTORNEY.

Dec. 6, 1966 H. E. VON ROSENBERG 3,290,405

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am mokudmm wON ATTORNEY United States Patent 3,290,405 PRODUCTION OF ISOOLEFINS Hermann E. van Rosenberg, Baytown, Tex., ass1gn0r, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Filed Nov. 7, 1962, Ser. No. 235,951 Claims. (Cl. 260-6832) The present invention relates to the production of isoolefins by the catalytic cracking of a hydrocarbon feed stock. More particularly, the present invention deals with the maximization of isoolefin production from hydrocarbon feed stocks by catalytically cracking the feed stock in a transfer line reactor, separating the isoolefins from the cracked product, and re-equilibrating selected olefin portions of the cracked hydrocarbon product.

The use of light olefin hydrocarbons for chemical raw materials is increasing each year. The primary source for these olefins is catalytic cracking in petroleum refineries. Particularly desirable isoolefins, isobutylene and the Z-methyl butenes, are present in a gaseous product from the catalytic reaction in almost thermodynamic equilibrium with the isomers of like carbon content. It has been found that a subsequent transfer line catalytic treatment of the normal olefins remaining after removal of the isoolefins from the catalyticall'y' cracked product stream will re-equilibrate the isoolefins; i.e., supply the thermodynamic equilibrium amounts of isoolefins by reaction of the normal olefins. The competing side reactions such as cracking and polymerization are minimized by controlling the residence time during re-equilibration.

Light isoolefin production is maximized by obtaining from any source a C or C stream which includes normal olefins, isoolefins, and paraffins, removing at least a portion of the isoolefins from the stream, and re-equilibrating the isoolefins-attenuated stream (i.e., having less than thermodynamic equilibrium quantities of isoolefin) to produce more isoolefins. The C or C stream is preferably obtained from a catalytically cracked hydrocarbon stream, and the re-equilibration is accomplished by passing the isoolefin-attenuated stream over a silica-alumina cracking catalyst at a catalyst-to-oil ratio of 2.5:1 to 25:1, preferably 5:1 to :1, at a temperature within the range of 850 F. to 1050 F. Competing reactions are controlled by conducting the reaction in a transfer line reactor so that residence time may be rigorously controlled. The contact time must be kept below 5 seconds if competing reactions are to be minimized.

The contact time of the isoolefin-attenuated stream may be controlled by limiting the actual residence time within the reaction zone or by adding fresh feed or other hydrocarbon streams .at the appropriate point in the transfer line reaction zone. The addition of fresh feed lowers the temperature, dilutes the re-equilibrated stream, and thereby diminishes theefiect of competing reactions. The fresh feed or other hydrocarbon stream may be admixed with the re-equilibrated stream in a ratio of 1:1 to 20:1

by volume. Although these side reactions are minimized by the practice of the present invention, they do occur to some extent and the products thereof should be separated from the prime stream containing the equilibrium quantity of the various olefin isomers. Therefore, it is preferred that the re-equilibration will be followed by a fractionating column or the equivalent thereof in order to produce a prime stream containing the desired C or C olefin isomers.

Thus, re-equilibration may be accomplished by using a dual zone reactor and recycling a portion of the light olefin streams, or by using a second, separate reactor in series with the primary reactor.

The present invention is shown more particularly in the drawings wherein:

3,290,405 Patented Dec. 6, 1966 Referring now to FIG. 1, wherein a preferred mode of practicing the present invention is set forth, a reactor having a first zone 120 and a second zone 102 is shown. A virgin hydrocarbon feed stock boiling within the range of about 500 F. to about 1200 F. is introduced into the catalytic cracking reactor 100 by means of line 101, into the second zone 102 wherein the feed stock is contacted with a catalytic cracking catalyst such as silica-alumina at a temperature within the range of 850 F. to 1050 F. and for a time period within the range of l to 10 seconds. The reaction products are passed from zone 102 by way of line 104, quenched to a temperature of about 800 E, if desired, by means of a quench stream of water, steam, etc., introduced by way of line 106, and passed to a separator 108. The catalyst is separated from the hydrocarbons by means of a stripping section and introduced by way of line 112 into a regenerator 114. The catalyst is carried through line 112 by a stream of air introduced by way of line 116 which also provides at least a portion of the oxygen necessary for the combustion of carbon lay-down for the regeneration of the catalyst. The catalyst is returned by way of line 118 into first zone 120 of the reactor 100 as it will be more fully set forth hereinafter.

The hydrocarbon products from the separator 108 are discharged by way of line 122 into fractionating means 124 and 126 which are schematically shown as comprising two distillation columns, although it is to be understood that one or more distillation columns may be used. Extraction means may :be substituted for column 126, using sulfuric acid (for example) to separate the tertiary olefins from the remaining hydrocarbons. The hydrocarbons are separated into a heavy portion discharged by way of line 128 and a light hydrocarbon fraction containing C or C isomers which is discharged by way of line 130 for further separation into the isoolefins and the normal olefins and parafiins. Selected parts of the heavy portion may be recycled if desired into reactor 100 by means of line 128 controlled by valve 129 into zone 102 with the virgin feed.

The desired isoolefin portion is removed by way of line 132, for example, while the remainder of the stream is passed from the separating means by way of line 134. The separated isoolefins are removed for recovery while the normal olefins and paraflins are recycled by way of line 134 into the first zone 120 of the reactor 100. The recycle stream is contacted in zone 120 with the hot catalyst for 0.5 to 5 seconds at temperatures within the range of 850 F. to 1050 F. and the total efliuent from the-first zone is passed to the second zone 102. The fresh feed introduced into the second zone 102 by way of line 101 serves as a partial quench or diluent to reduce the side reactions of the re-equilibrated olefin recycle stream from zone 120. The fresh feed may be virgin gas oil or other suitable cracking feed stock, and is introduced in a ratio from 1:1 to 20:1 by volume with respect to the olefin recycle in line 134. For balanced operations, the olefin recycle should be from 10% to 40% (by volume) of the fresh feed. During the passage through the zone 120, the isomerization of the olefins in the recycle stream is accomplished to provide a roughly thermodynamic equilibrium distribution of isomers in the selected olefin cut. This equilibrium is not disturbed by passage through the zone 102. By selecting the amount of recycle, the degree of equilibration based on fresh feed may be adjusted, which in turn will determine the isoolefin production based on fresh feed.

Referring now to FIG. 2, an alternative method of practicing the present invention utilizing separate catalytic cracking facilities for the reequilibration is schematically set forth. A first react-or 200 is provided wherein a virgin feed is introduced by way of line 201and admixed with hot catalyst which is introduced into the reaction zone by way of line 202. The reaction within the reactor 200 is carried out at a temperature 'between 850 F. and 1050 F. with a hydrocarbon residence time within the range of seconds to 15 seconds. The effiuent from reactor 200 is passed by way of line 204 and quenched, if desired, by a water or steam injection, for example, 'by way of line 206, and is introduced into separator 20 8. The catalyst falls from separator 208 through a stripping zone 210, is admixed with air introduced by way of line 212, and is carried in admixture therewith by way of line 214 into a regenerator 216 wherein the catalyst is regenerated by burning the carbon from the surface thereof. The hydrocarbon from separator 208 flows by way of line 218 and line 220 into a 'fractionating tower 222 (schematically shown as one column although two are preferred). Tower 222 effects the separation of the hydrocarbon product into several streams: the bottom stream 224, side streams 226 and 228, and an overhead stream 230. A selected side stream 232 is removed which may, for example, comprise the butanes and butylenes produced by the catalytic reaction in reactor 200. These butylenes may be suitably separated by means of sulfuric acid extraction in extractor 234, with the isobutylenes being removed by way of line 236 for further purification and recovery with the normal butenes and butanes being introduced by way of line 238 into a second reactor 250. In reactor 250, catalyst is provided by way of line 252 and the reaction is carried out at a temperature within the range of 850 F. to 1050 F., with a hydrocarbon residence time of 0.5 second to 5 seconds. If desired, a quench stream such as catalytic cycle oil, light process gas oil, extracted cycle stock or other low metal content hydrocarbon streams may be introduced by way of line 254 in order to control the time period of contact at the elevated temperatures. Use of a low metal stream helps to maintain high catalyst activity. The quench stream to olefin stream ratio is desirably within the range from 1:1 to :1 if a quench is used. However, it is preferred to size the reaction zone 250 to give the desired residence time and to avoid use of a quench stream in order to minimize the size of separation equipment downstream of the reactor. Alternatively, the temperature-time relationship may be controlled in the outlet line 256 'by a steam or water, etc., quench stream introduced by way of line 258. The hydrocarbon and catalyst mixture is introduced into a separator 260, whence the catalyst is removed by Way of 'a stripper 262 and is passed vi-a line 266 in admixture with the air introduced by way of line 264 into a regenerator 268, whence catalyst is returned as aforesaid by way of line 252. The hydrocarbon products from the separator may be discharged by way of line 270 controlled by valves 272 and 274 for passage in admixture with the hydrocarbon from line 218 for separation in the fractionating tower 222, or valve 272 may be closed and the hydrocarbon stream passed by w-ay of line 276 controlled by valve 278 for separation in a fractionating tower 280, from whence a light gaseous product is withdrawn by way of line 282 and a heavy (polymerized) product may be withdrawn by way of line 284. It is to be understood that the side stream which comprises the intermediate boiling portion 286 is withdrawn by way of line 270 for further separation in the fractionating tower 222 and extractor 234, or if the fractionator 280 (of two towers) is being used, the valve 274 may be closed and the hydrocarbon stream may bypass the fractionator 222 and be passed by way of line 290 controlled by valve 292 directly into the extractor 234 for separation of the isoolefins from the normal olefins and paraflins.

It is to be stressed that in the reactor 250, the isobutylene is re-equilibrated (at about 950 F.) to an amount of about 37 mol percent of the butylenes removed from that reaction zone, so that the net recovery of isobutylene is increased. It should further be noted that a continuous recycle of the normal butylenes is accomplished by the use of the scheme of FIG. 2, similar to that experienced in FIG. 1, whereby the production of the normal olefin product is minimized concurrently with the maximization of recovery of the isoolefins.

As exemplary of the practice of the present invention, the following examples are set forth.

Example I From a catalytically cracked hydrocarbon product stream, a C olefin hydrocarbon stream is obtained which contains 37% isobutylene, 63% normal butylenes, and no butanes. The isobutylene is selectively removed by contacting the C stream at 65 F to 100 F. with 65 weight percent sulfuric acid to produce an isoolefin-attenuated raflinate containing 8% isobutylene and 92% normal butylenes.

The raflinate is passed through a reaction zone in contact with 13% silica-alumina cracking catalyst at a temperature of about 950 F. and for a contact period of 0.6 second whereby the normal butylenes are isomerized to produce nearly thermodynamic equilibrium amounts of isobutylene. The re-equilibrated stream contains 33% isobutylene and 67% normal butylenes, a 90% approach to thermodynamic equilibrium. Losses to carbon, light gases, butanes, and heavier materials total only 4%.

The re-equilibrated stream is recycled (recycle ratio 1.96) to the sulfuric acid extraction Zone and processed in admixture with the fresh C olefinic hydrocarbons as detailed in FIG. 2. By the present invention, 87% isobutylene is produced from the C olefinic hydrocarbon stream as opposed to 31% recovery in a one-pass operation.

Example II A catalytically cracked product comprising 5 carbon atom, olefinic hydrocarbons is obtained and found to comprise about 58% Z-methyl butenes. The Z-methyl butenes are removed by contacting with 65% sulfuric acid at 50 F. to obtain a rafiinate phase containing 18% Z-methyl butenes with an recovery of 95% purity Z-methyl butenes. This rafiinate phase is passed through a transfer line catalytic cracking reaction zone in contact with a silica-alumina catalyst at a temperature of 925 F. with a contact time of 0.6 second. The effluent stream is passed to a separator wherein the catalyst is passed from the hydrocarbon stream, and the hydrocarbon stream is then analyzed and found to contain about 53% Z-methyl bu tenes, a 90% approach to equilibrium. This re-equilibrated stream is then recycled as in Example I at a recycle ratio of 0.93. The recovery of Z-methyl butenes by the practice of the present invention increases Z-methyl butenes production from about 50% to about 91%, based on the pentylene feed.

The butenes at 950 P. will re-equilibrate to produce essentially the thermodynamic equilibrium amount of isobutylene: about 37 mol percent of C olefins in the stream. The C olefins at 950 F. in the cracking zone will reequilibrate to a composition of about 58 mol percent 2- methyl butenes: 40 mol percent of 2-methyl-2-butene and 18 mol percent of Z-methyl-l-butene. Thus, it is ap parent that by re-equilibrating the normal olefins in the product stream 'from catalytic cracking reaction, the output and recovery of isoolefins may be maximized and substantial economic benefits will be realized.

It should be understood that in the practice of the present invention, the initial catalytic cracking may take place in a transfer line reactor, in a dense phase reactor, or in a moving bed type reactor, whereas the re-equilibration reaction will take place more desirably in a transfer line type of catalytic cracking reactor.

Applicant having set forth in detail the essence of the present invention, and having set forth a preferred and best mode of practicing the invention, what is desired to be protected by Letters Patent should be determined not from the specific examples herein given, but rather by the appended claims.

I claim:

1. A method which comprises passing a hydrocarbon feed stock into the sec-nd zone of a transfer line reactor comprising a first zone and a second zone, contacting said feed stock in said second zone with a cracking catalyst at a temperature within the range of 850 F. to 1050 F. and a time period within the range of about 1 to about 10 seconds, passing said catalyst and the reacted hydrocarbon into a separation zone, separating said catalyst from said hydrocarbon, separating said hydrocarbon into fractions including a light hydrocarbon fraction including an isoolefin and a normal olefin, separating said light hydrocarbon fraction into an isoolefin fraction and an isoolefin-attenuated fraction, passing said isoolefin-attenuated fraction into said first zone into contact with cracking catalyst at a temperature within the range of 850 F. to 1050 F., at a catalyst to oil ratio within the range from 2.5 :1 to 25:1, and for a time period within the range of 0.5 second to about 5.0 seconds to obtain a re-equilibrated stream, and passing all of said catalyst and said re-equilibrated stream into said second zone, thereby maximizing the production of isoolefins.

2. A method in accordance with claim 1 wherein said light hydrocarbon fraction comprises butylenes.

3. A method in accordance with claim 1 wherein said light hydrocarbon fraction comprises pentylenes.

4. A method in accordance with claim 1 wherein said separation of isoolefins from the light hydrocarbon fraction is accomplished by sulfuric acid extraction.

5. A method in accordance with claim 1 wherein the volume ratio of said hydrocarbon introduced into said said second zone to said isoolefin-attenuated fraction is within the range from 1:1 to 20:1.

References Cited by the Examiner UNITED STATES PATENTS 2,217,252 10/1940 Hoog 260-6832 2,301,342 11/1942 Sumerford et -al. 260-6832 2,386,468 10/1945 Ipatieff et al. 260-6832 2,410,316 10/ 1946 Thomas 208- 2,415,530 2/ 1947 Porter 208-70 2,434,634 1/ 1948 Bates 208-70 2,438,456 3/ 1948 Russell et a1 208-70 2,495,648 1/1950 Voge et al 260-6832 2,982,717 4/ 1961 Waddill 208-159 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

C. E. SPRESSER, Assistant Examiner. 

1. A METHOD WHICH COMPRISES PASSING A HYDROCARBON FEED STOCK INTO THE SECOND ZONE OF A TRANSFER LINE REACTOR COMPRISING A FIRST ZONE AND A SECOND ZONE, CONTACTING SAID FEED STOCK IN SAID SECOND ZONE WITH A CRACKING CATALYST AT A TEMPERATURE WITHIN THE RANGE OF 850*F. TO 1050*F. AND A TIME PERIOD WITHIN THE RANGE OF ABOUT 1 TO ABOUT 10 SECONDS, PASSING SAID CATALYST AND THE REACTED HYDROCARBON INTO A SEPARATION ZONE, SEPARATING SAID CATALYST FROM SAID HYDROCARBON, SEPARATING SAID HYDROCARBON INTO FRACTIONS, INCLUDING A LIGHT HYDROCARBON FRACTION INCLUDING AN ISOOLEFIN AND A NORMAL OLEFIN, SEPARATING SAID LIGHT HYDROCARBON FRACTION INTO AN ISOOLEFIN FRACTION AND AN ISOOLEFIN-ATTENUATED FRACTION, PASSING SAID ISOOLEFIN-ATTENUATED FRACTION INTO SAID FIRST ZONE INTO CONTACT WITH CRACKING CATALYST AT A TEMPERATURE WITHIN THE RANGE OF 850*F. TO 1050*F., AT A CATALYST TO OIL RATIO WITHIN THE RANGE FROM 2.5:1 TO 25:1, AND FOR A TIME PERIOD WITHIN THE RANGE OF 0.5 SECOND ABOUT 5.0 SECONDS TO OBTAIN A RE-EQUILIBRATED STREAM, AND PASSING ALL OF SAID CATALYST AND SAID RE-EQUILIBRATED STREAM INTO SAID SECOND ZONE, THEREBY MAXIMIZING THE PRODUCTION OF ISOOLEFINS. 